Why worry
about pipe size in a residential irrigation system?
Correct pipe sizing leads to a more
efficient distribution of water throughout the irrigated
area, by sizing pipe correctly you will have less
runoff, and even application of water (less swampy
wet spots). In addition the likelyhood of water
hammer is greatly reduced when operating at 5 FPS
or less IE: less broken sprinkler lines and fittings,
greater life expectancy on valves & other components.
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Doesn’t
reducing pipe size build pressure?
NO! This is a quite common misconception. Friction
loss and Elevation Changes are what cause pressure
loss in piping systems, factors which contribute to
friction loss are:
#1 Inside diameter
#2 Pipe Material (IE: PVC, Galvanized, Copper, Polyethylene)
#3 Flow in Gallons Per Minute
#4 Length of pipeline
#5 Changes in flow direction (Fittings)
A good rule of thumb for elevation is 1/2 psi loss
(or gain) for every foot of elevation. Gaining elevation
you lose pressure, losing elevation you gain pressure.
(actual loss is .433 psi)
When sizing pipe always remember BIGGER IS BETTER!
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My sprinklers
don't spray as far as they should. My sprinklers
don't pop-up.
If a sprinkler does not spray its rated distance,
it is usually due to a lack of pressure. Sprinklers
have an optimum pressure range at which they perform
as specified. If the pressure at the sprinkler is
too low, then the sprinkler does not spray as far
as it should. The common remedies are to put bigger
nozzles on the sprinklers or to add more sprinklers.
Both of these "remedies" further lower the pressure
and compound the problem. One needs to do is ask
the question.
Did the system perform correctly when it was originally
installed?
Yes? Then something has changed
- usually something is worn or broken
-
Broken riser, pipeline or sprinkler
- Worn out seals on pop-up sprinklers
- Other possibilities are worn out automatic valves
or debris plugging the sprinkler screens
- Occasionally the problem is on the supply side of
the system, possibly a pump that is not working
correctly or a reduction in pressure from the water
purveyor.
No? The source of water is not large
enough to satisfy the demand of the system. Assuming
there is enough pressure available to run a properly
designed system, the system must be redesigned with
lower flow rates. Either valves must be added or nozzle
sizes can be reduced. Take care when reducing nozzle
sizes that you still get the distance required to
efficiently irrigate your area.
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